Anaerobic digester employing circular tank

ABSTRACT

A method and apparatus for the anaerobic digestion of high-solids waste material. The apparatus includes a closed container having a relatively circular outer wall. The closed container has a first passage having an inlet in which the waste material flows in a first direction, a second passage in which the waste material flows in a second direction, and a divider having an end. The divider separates the first passage from the second passage, such that the waste material flows around the end of the divider when flowing from the first passage to the second passage.

FIELD

The invention relates to waste-processing systems for processing organic waste material.

BACKGROUND

Many prior art waste-processing systems are designed for low-solids waste, such as municipal waste, that has a solids content of approximately one percent. High-solids wastes such as manure that have a solids content of approximately five to twelve percent either clog the system or are insufficiently processed. The processing of high-solids waste has typically been performed using a plug flow process that is characterized by a straight-through system.

Prior art waste-processing systems for either high- or low-solids waste use large amounts of purchased energy in the form of electricity or natural gas to generate heat and run pumps to process the wastes because these systems typically exhibit inefficient heating of the waste as it is processed. In addition, prior art waste-processing systems have the added problem of disposing of the products of their processing. It is anticipated that stricter environmental regulations will limit the amount of waste than can be applied to fields as fertilizer because of the phosphates and nitrogen content of the waste. As fields reach their limits, other fields must be found. As the amount of unfertilized land dwindles, either other outlets for waste must be found, or a disposal method that meets the stricter environmental regulations must be developed and used.

SUMMARY

In one embodiment, the invention provides a method for the anaerobic digestion of high-solids waste material. The method may include providing a closed container having a relatively circular outer wall. The closed container may include a first passage having an inlet in which the waste material flows in a first direction, a second passage in which the waste material flows in a second direction and a divider having an end. The divider may separate the first passage from the second passage, with the waste material flowing around the end of the divider when flowing from the first passage to the second passage.

In another embodiment the invention provides an anaerobic digester for digesting high-solids waste material. The anaerobic digester may include a relatively circular closed container having a first passage in which the waste material flows in a first direction and a second passage in which the waste material flows in a second direction relatively opposite the first direction. The first passage may be separated from the second passage by a divider.

In another embodiment, the invention provides a closed anaerobic digester for digesting high-solids waste material. The anaerobic digester may include a first section configured to receive the waste material from a source outside of the closed anaerobic digester and to preheat the waste material. The first section may have an outer perimeter formed at least in part in the shape of a circle. The anaerobic digester may further include a second section configured to receive the preheated waste material from the first section and to anaerobically digest the preheated waste material. The second section may have a first passage and at least one second passage separated from the first passage by one or more dividers. The waste material may change direction upon flowing from the first passage to the at least one second passage. The second section may have an outer perimeter formed at least in part in the shape of the circle.

Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a waste processing system according to one embodiment of the invention.

FIG. 2 is a partial cross-section elevational view of the digester of the waste processing system shown in FIG. 1.

FIG. 3 is a cross-section elevational view of a wall between a mixing chamber and the digester and taken along the 3-3 line of FIG. 1.

FIG. 4 is a partial cross-section elevational view of a clarifier, taken along the 4-4 line of FIG. 1.

FIG. 5 is a perspective view of a composter of the waste processing system shown in FIG. 1.

FIG. 6 is a cross-sectional view of the composter taken along the 6-6 line in FIG. 5.

FIG. 7 is a flowchart of the process employed in the waste processing system shown in FIG. 1.

FIG. 8 is a view similar to FIG. 7 and shows an alternative process of the invention.

FIG. 9 is a view similar to FIGS. 7 and 8 and shows another alternative process of the invention.

FIG. 10 is a view similar to FIGS. 7-9 and shows another alternative process of the invention.

FIG. 11 is an enlarged view of a portion of the waste processing system shown in FIG. 1.

FIG. 12 is a schematic view of an alternative waste processing system embodying the invention.

FIG. 13 is a partial cross-sectional view of a digester taken along the 13-13 line in FIG. 12.

FIG. 14 is a partial cross-section elevational view of the digester taken along the 14-14 line in FIG. 12.

FIG. 15 is a schematic view of a waste processing system according to one embodiment of the invention.

FIG. 16 is a schematic view of a waste processing system according to another embodiment of the invention

DETAILED DESCRIPTION

Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

A waste-processing system 10 embodying the invention is illustrated in FIGS. 1-10. FIGS. 1-6 show the apparatus in which the process is conducted. The system 10 is described in terms of processing manure, but may also be used to process wood pulp, municipal wastes, or organic waste products in general.

FIG. 1 shows schematically the apparatus used to process high-solids farm waste. A digester enclosure 20 includes three major sections: a mixing chamber 30, a digester 40, and a clarifier 50. The digester enclosure 20 is arranged such that a relatively large digester 40 may be built in relatively small space.

FIG. 2 illustrates the construction of an outside wall 54 of the digester enclosure 20. The height of the outer wall 54 of the digester enclosure 20 is approximately 17 feet, with a liquid depth 58 in the digester enclosure 20 of approximately 14 feet and a biogas storage area 59 of about 18 inches above the liquid 58. A footing 62 provides an interface between the wall 54 and the ground 66, and supports the wall 54 and the edge 70 of the floor 74. Both the footing 62 and the wall 54 are constructed of poured concrete. The wall 54 is approximately twelve inches thick at the lower end 78 of the wall 54, and approximately eight inches thick at the upper end 82 of the wall. The floor 74 of the digester enclosure 20 is approximately four inches of concrete. Insulation 86 with a thickness of approximately four inches may be arranged below the floor 74 and provides an interface between the floor 74 and the ground 66.

The roof 90 of the digester enclosure 20 is located approximately 15 feet, 8 inches above the floor 74 of the digester enclosure 20. The roof 90 is constructed of an approximately ten-inch thickness 98 of SPANCRETE concrete topped by a layer of insulation 94 with a thickness between four and eight inches, and more particularly, between three and four inches.

A bio gas storage chamber 102 may be located above the roof 90. The primary component of the chamber 102 is a liner 106 including an upper liner section 110 and a lower liner section 114. The liner 106 is preferably constructed from high-density polyethylene (HDPE), but may be any other suitable material. The liner 106 is sealed around the edges 118 of the liner 106 by capturing the edges 118 beneath six-inch channel iron 122, which is removably attached to the digester enclosure walls 54 using nuts 126 on a plurality of anchor bolts 130 embedded in the digester enclosure wall 54. A ten-inch PVC pipe 134 is inserted around the periphery of the chamber 102 within the liner 106 to assist in maintaining the seal around the periphery of the liner 106. The liner 106 is constructed such that it can flexibly fill with bio gas as the bio gas is produced in the digester 40, and can be emptied of bio gas as is needed. The bio gas storage chamber 102, as an addition to biogas storage 59 within the digester enclosure 20, may be replaced by any other suitable gas storage system including a roofed storage system.

Returning to FIG. 1, the mixing chamber 30 has horizontal dimensions of approximately 36 feet by 15 feet. Arranged within the mixing chamber 30 is approximately 2000 feet of three or four-inch black heating pipe 142, which is designed to carry hot water to heat sludge 144 within the mixing chamber 30. An influent pipe 148 carries manure 336 into the mixing chamber 30. The closed container may further include a heating device and may or may not include a partition. The heating device may comprise a conduit containing a liquid or gas with discharge nozzles to further agitate the waste material, positioned to heat waste material to form heated waste material. Mixing within the mixing chamber 30 is provided by at least one of a system of mixing nozzles utilizing recirculated biogas (the nozzles being on the end of an activated sludge recirculation pipe 147) and convective flow resulting from the heating of the manure 336 by the heating pipe 142. In one embodiment, the recirculation pipe may deliver effluent to the digester 166, in another embodiment to the mixing chamber 30. If required, a standard auger 146 used for removing solids from the mixing chamber 30 is arranged near the floor 150 of the mixing chamber 30 such that it can transport solids from the floor 150 of the mixing chamber 30 through the wall 154 of the mixing chamber 30 and to a collection device 158. The collection device 158 is optional. In another embodiment (not shown), solids may be removed from the mixing chamber 30 by any other suitable system, such as a sump pump.

As illustrated in FIG. 3, a cutout 160 formed in the wall 162 between the mixing chamber 30 and the digester 40 allows sludge to flow from the mixing chamber 30 into the digester 40. In addition, removable panels 161 may be positioned to block opening 163 in the wall 162. The removable panels shown in FIG. 3 are optional. Removable panels 161 may be removed as needed to allow greater flow from mixing chamber 30 to digester 40, if desired.

Returning to FIG. 1, the digester 40 is a generally U-shaped tank with overall horizontal dimensions of approximately 100 feet long and 72 feet wide. A center wall 165 approximately 90 feet in length divides the digester 40 into the two legs 166, 170 of the U-shape. Thus each leg 166, 170 of the digester 40 is approximately 100 feet long and 36 feet wide.

The first leg 166 of the digester 40 includes approximately 800 feet of three or four-inch black heating pipe 174 through which heated water or gas can flow. The heating pipe 174 is or separate gas pipes are arranged along the center wall 165. The second leg 170 of the digester 40 includes approximately 200 feet of four-inch black heating pipe 178, which is also arranged along the center wall 165. In another embodiment illustrated in FIG. 11, the heating pipes 174, 178 or separate gas pipes 178 may include jet nozzles 180 to dispense heated gas or recycled biogas into the sludge 144.

In addition to producing activated sludge 184, the anaerobic digestion of the digester 40 also produces bio gas in the form of methane gas, which is collected in the space above the liquid in digester 40 and below the roof 98 and can also be stored in the gas storage chamber 102. Any liquid that condenses within the chamber 102 is directed through the effluent pipe 196 (see FIGS. 7-9) to the liquid storage lagoon 198 (see FIGS. 7-9). The collected bio gas is used to fuel an internal combustion engine 138 (see FIG. 7) that, in combination with an electric generator, is used to produce electricity that is sold to a power utility 332 (see FIG. 7). The cooling system of the internal combustion engine 138 also produces hot coolant that is used for heating and agitation in the mixing chamber 30 and, alternatively, for heating and agitation in the mixing chamber 30 and digester 40. Hot water from the engine 138 passes through an air/water cooler 334 (see FIG. 7) to reduce the temperature of the water from the approximately 180° F. temperature at the exit of the engine 138 to approximately 160° F. for use in the mixing chamber 30 and the digester 40.

As shown in FIG. 1, the optional clarifier 50 is located adjacent the digester 40 beyond clarifier panels 182 and adjacent the mixing chamber 30. The clarifier 50 has horizontal dimensions of approximately 36 feet by 21 feet, and is largely empty of any equipment or hardware, with the exception of an equipment room 183. Turning to FIG. 4, the clarifier panels 182 are constructed from HDPE and form a partial barrier between the digester 40 and the clarifier 50. The clarifier panels 182 cover the entire horizontal dimension across the clarifier 50 from center wall 165 to outer wall 54. Separation panels 186 within the clarifier 50 serve to direct solids in a downward direction to the bottom 190 of the clarifier 50, where the solids collect in a sump 194. Sump pipe 198 leads to a standard solids press 214 (see FIGS. 7-9), and to the activated sludge recirculation pipe 147 carrying activated sludge 184 to the mixing chamber 30, or, alternatively, the digester 40 (see FIG. 1).

As illustrated in FIGS. 7-9, a portion of the liquid produced as a result of the operation of the solids press 214 may be recycled to the mixing chamber 30 or the digester 40 for further processing.

Returning to FIG. 4, liquids in the clarifier 50 decant through gap 202 and collect in a liquid sump 206. A liquid effluent pipe 210 within the liquid sump 206 leads through a heat exchanger 340 (see FIG. 7) and to a liquid storage lagoon 198 (see FIG. 7).

A composter 220 as illustrated in more detail in FIGS. 5 and 6 is located downstream of the solids press 214. The composter is optional. The primary components of the composter 220 include a water tank 224 and a composting barrel 228. The water tank 224 is generally a rectangular parallelepiped with six-inch-thick walls 230 constructed from concrete. A four-inch layer of insulation 232 (not shown in FIG. 6) covers the periphery of the walls 230. A sump 236 is located in the floor 240 of the water tank 224. Extending through the floor 240 of the water tank 224 is an air supply pipe 244. A port 248 in the first wall 252 of the water tank 224 accommodates a sludge supply pipe 256 that connects the solids press 214 with the composter barrel 228. A port 260 in the second wall 264 of the water tank 224 accommodates a composter solids exit pipe 268.

The water level 272 of the water tank 224 may be varied to provide buoyant support to the composter barrel 228; the water level 272 as illustrated in FIGS. 5 and 6 is representative of a typical level. The water 276 is typically at 140-160° F. A water inlet pipe 280 provides a flow of water 276 to the composter barrel 228 and the water tank 224. The water 276 is supplied from the cooler 334 of engine 138.

The composter barrel 228 defines an interior chamber 232. A sludge supply auger 284 is located within the sludge supply pipe 256 and extends from within the sludge supply pipe 256 into chamber 232 of the barrel 228. A composted solids exit auger 288 extends from within chamber 232 of barrel 228 into the composter solids exit pipe 268. Each pipe 256, 268 is connected to the ends 292, 294 of the composter barrel 228 using a double rotating union seal with an internal air pressure/water drain (not shown). The pipes 256, 268 and augers 284, 288 are designed such that air that is necessary for drying the sludge and for aerobic digestion may pass through the composter barrel 228. Air passes through solids exit pipe 268 and air inlet pipe 266, into the composter barrel 228, and out through air outlet pipe 258 and sludge supply pipe 256. The air pipes 258, 266 extend vertically to keep their ends 270 above the activated sludge 184 in the composter barrel 228.

The composter barrel 228 is generally cylindrical and approximately 100 feet long and 10 feet in diameter. A plurality of wear bars 296 is attached to the exterior circumference of the barrel 228. Rubber tires 300 acting on the wear bars 296 serve to hold the composter barrel 228 in position.

As illustrated in FIGS. 5 and 6, a plurality of vanes 304 is attached to the barrel 228. These vanes 304 extend between the third and fourth wear bars 308, 312. The vanes 304 are generally parallel to the longitudinal axis of the composter barrel 228. As shown in FIG. 6, to effect cooperation with the vanes 304, the water inlet pipe 280 and the air inlet pipe 244 are laterally offset in opposite directions from the vertical centerline of the composter barrel 228. As a result, when water 276 flows from the water inlet pipe 280, the water 276 collects on the vanes 304 on a first side 316 of the composter barrel 228, and when air 320 flows from the air inlet pipe 244, air 320 collects under the vanes 304 on a second side 318 opposite the first side 316 of the composter barrel 228. The lateral imbalance resulting from weight of water 276 on the first side 316 of the barrel 228 and the buoyancy of the air 320 on the second side of the barrel 228 causes the barrel 228 to rotate in a clockwise direction as viewed in FIG. 6.

The composter barrel 228 is slightly declined toward the exit end 294 of the composter barrel 228 to encourage the activated sludge 184 within the composter barrel 228 to move along the longitudinal axis of the composter barrel 228 toward the exit end 294. As shown in FIG. 6, the composter barrel 228 also includes internal baffles 296 that serve to catch and turn the activated sludge 184 as the composter barrel 228 rotates.

As illustrated in FIG. 1, the composter solids exit pipe 268 connects to a standard bagging device 324 that places the composted solids into bags 328 for sale.

In operation of the waste-processing system 10, as illustrated in FIGS. 1 and 7, unprocessed cow manure 336 from area farms and other sources is transported to the waste processing site and transferred to a heat exchanger 340 where, if necessary, the manure 336 is thawed using warm water from the clarifier 50 by way of liquid effluent pipe 210.

Manure 336 is then transferred from the heat exchanger 340 to the mixing chamber 30 through influent pipe 148, where the manure 336 may, alternatively, be mixed with activated sludge 184 recycled from the clarifier 50 by way of activated sludge recirculation pipe 147 to become sludge 144. The sludge 144 is heated to approximately 95-130° Fahrenheit by directing coolant at approximately 160° F. from the engine cooler 334 through the mixing chamber heating pipes 142. In addition, if required, solids such as grit fall to the bottom of the mixing chamber 30 under the influence of gravity and are removed using the mixing chamber auger 146. The solids are then transferred to a disposal site.

After a stay of approximately one day in the mixing chamber 30, the sludge 144 flows through cutout 160 or opening 163 in the wall 162 and into the digester 40, where anaerobic digestion takes place. The activated sludge 184 added to the manure 336 in the mixing chamber 30 or digester 40 serves to start the anaerobic digestion process.

The apparatus and method described herein employ modified plug flow or slurry flow to move the sludge, unlike the plug flow in prior art systems. The digester heating pipes 174, 178 locally heat the sludge 144 using hot water at approximately 160° F. from the cooler 334 of the engine 138, causing the heated mixed sludge to rise under convective forces. The convection develops a current in the digester 40 that is uncharacteristic of prior art high-solids digesters. Sludge 144 is heated by the digester heating pipes 174, 178 near the digester center wall 165, such that convective forces cause the heated sludge 144 to rise near the center wall 165. At the same time, sludge 144 near the relatively cooler outer wall 54 falls under convective forces. As a result, the convective forces cause the sludge 144 to follow a circular flow path upward along the center wall 165 and downward along the outer wall 54. At the same time, the sludge 144 flows along the first and second legs 166, 170 of the digester 50, resulting in a combined corkscrew-like flow path for the sludge 144.

In another embodiment (not shown), hot gas injection jets using heated gases from the output of the engine 138 replace the hot water digester heating pipes 174, 178 as a heating and current-generating source. The injection of hot gases circulates the sludge 144 through both natural and forced convection. A similar corkscrew-like flow path is developed in the digester 40.

As shown in FIG. 11, to further increase upward flow of the heated sludge 14 near the center wall 165, biogas may be removed from the biogas storage area 59 in the digester 40, pressurized with a gas centrifugal or rotary-lobe blower, and injected into the heated sludge 144 through nozzles 376 positioned onto conduit 378. This recycled biogas injection near the floor 74 of the digester 40 serves to increase the rapidity of the cork-screw-like flow path for the heated sludge 144.

In the arrangement shown in FIG. 1, the U-shape of the digester 40 results in a long sludge flow path and thus a long residence time of approximately twenty days. As the sludge 144 flows through the digester 40, anaerobic digestion processes the sludge 144 into activated sludge 184. The anaerobic digestion process also reduces the phosphate content of the liquid effluent after solids removal, by approximately fifty percent, which is a key factor in meeting future environmental regulations.

From the digester 40 the activated sludge 184 flows into the optional clarifier 50. The clarifier 50 uses gravity to separate the activated sludge 184 into liquid and solid portions. Under the influence of gravity and separation panels 186, the liquid portion rises to the top of the mixture and is decanted through a gap 202 into a liquid sump 206. It is later transferred to lagoon storage 198 through effluent pipe 210. The liquid is then taken from the lagoon 198 for either treatment or use as fertilizer.

The solid portion of the activated sludge 184 settles to the bottom 190 of the clarifier 50 in sump 194. From there, approximately ten to twenty-five percent of the activated sludge 184 is recycled to the digester 40 or mixing chamber 30 through activated sludge recirculation pipe 147 to mix with the incoming manure 336, as described above. The remaining approximately seventy-five to ninety percent of the activated sludge 184 is removed from the clarifier 50 through sump pipe 198 and is transferred to the solids press 214 in which the moisture content of the activated sludge 184 is reduced to approximately sixty-five percent.

From the solids press 214, the activated sludge 184 is transferred through sludge supply pipe 256 using sludge supply auger 284 to the interior chamber 232 of the composter barrel 228 where the activated sludge 184 is heated and agitated such that aerobic digestion transforms the activated sludge 184 into usable fertilizer. Outside bulking compost material can be added to the chamber 232 to make the fertilizer more suitable for later retail sale. As the composter barrel 228 turns, baffles 296 within the chamber 232 agitate and turn the sludge. This agitation also serves to aerate the sludge to enhance aerobic digestion. At the same time, the tank of water 224 in which the barrel 228 sits heats the barrel 228. This heating also promotes aerobic digestion.

In the preferred embodiment, water 276 falling from the water inlet pipe 280 and air 320 rising from the air inlet pipe 244 collects on the vanes 304 and causes the composter barrel 228 to turn around its longitudinal axis. In other embodiments, direct motor or belt drives, or any other suitable drive mechanism may turn the composter barrel 228.

As the activated sludge 184 turns over and undergoes aerobic digestion in the chamber 232, it also travels longitudinally and eventually exits the composter barrel 228 through the composter solids exit pipe 268, driven by the composter solids exit auger 288. The processed sludge, which has become usable fertilizer at approximately forty-percent moisture, is transferred to a bagging device 324. In the bagging device 324, the processed sludge is bagged for sale as fertilizer.

In an alternative embodiment illustrated in FIG. 8, a turbine 139 replaces the internal combustion engine as described above. The turbine 139 is preferably an AlliedSystems TURBOGENERATOR turbine power system as distributed by Unicorn Distributed Energy, but may be any other suitable turbine. The turbine 139 is fueled by the methane collected in the bio gas storage chamber 59 or 102. The differences with the use of a turbine 139 from the previously-discussed process are outlined as follows. Instead of an engine cooler 334 producing heated coolant, the turbine 139 produces exhaust gases at approximately 455° F. The hot exhaust gases are used to heat water in a closed loop 335 through an air/water heat exchanger 337. The heated water is then used for heating in the mixing chamber 30 and for heating and agitation in the digester 40. This embodiment is used in conjunction with a composter (not shown) as described above.

As shown in FIG. 8, the composter is replaced with a solids dryer 218 in which hot exhaust from the turbine 139 or reciprocating engine 138 is used to dry the sludge taken from the solids press 214. From the solids dryer 218, the activated sludge 184 is transferred to a bagging device 324. In the bagging device 324, the processed sludge is bagged for sale as fertilizer.

In another embodiment illustrated in FIG. 9, hot exhaust gases from the turbine 139 are used to heat methane from the bio gas storage chamber 102 to approximately 160° F. in an air/air heat exchanger 220. The heated methane is then injected into the mixing chamber 30 and the digester 40 for heating and agitation. In this embodiment, it is possible to seal off the digester 40 from any air contamination because only methane is used for heating and agitation. The methane is then recaptured in the bio gas storage chamber for reuse. This embodiment is used in conjunction with a composter (not shown) as described above.

In the embodiment illustrated in FIG. 9, the composter is replaced with a solids dryer 218 in which hot exhaust from the turbine 139 is used to dry the sludge taken from the solids press 214. Again, from the solids dryer 218, the activated sludge 184 is transferred to a bagging device 324. In the bagging device 324, the processed sludge is bagged for sale as fertilizer.

In still another embodiment illustrated in FIG. 10, a fluidizing bed dryer 350 takes the place of the composter or solids dryer described in previous embodiments. Pressed bio solids at approximately 35 percent solids from the solids press 214 enter the fluidizing bed dryer 350 where the solids are fluidized using heated air in a closed-loop air system 354. This fluidizing results in moisture from the bio solids being entrained in the heated air. The moisture-laden heated air passes through a water condenser 358 where water is removed from the heated air and circulated back to the heating pipe 142 in the mixing chamber 30 and to the heating pipe 174 in the digester 40. Heat is provided to the closed-loop air system 354 through an air/air heat exchanger 362. Hot exhaust gases from a series of turbines 139 provide heat to the air/air heat exchanger 362. The exhaust gases then enter the water condenser 358 to remove combustion moisture from the turbine exhaust before the remaining gases are vented to the atmosphere. The water condenser 358, in addition to recapturing water, also recaptures heat carried by the turbine exhaust and by the heated air in the closed-loop air system 354. This recaptured heat is used to heat the water circulating in the closed-loop water heating system.

The combination of a fluidizing bed dryer 350 and an air/air heat exchanger 362 recaptures heat produced by the turbines 139 that would otherwise be lost in the turbine exhaust. The heated air in the fluidizing bed dryer 350 evaporates water carried in the effluent from the solids press. The latent heat of vaporization carried by the moisture in the air leaving the fluidizing bed dryer 350 is substantially recaptured in the water condenser 358. The closed-loop air system 354 allows for air with reduced oxygen content to be used in the fluidizing bed dryer 350 to reduce the risk of fire associated with drying organic material. In addition, the closed-loop air system 354 allows for the addition of an auxiliary burner (not shown) if needed to process wetter material in the fluidizing bed dryer 350. A variable speed fan (not shown) can be added to the closed-loop air system 354 after the water condenser 358 to pressurize the air for the fluidizing bed dryer 350.

In the embodiment illustrated in FIG. 10, from the solids dryer 218, the activated sludge 184 is transferred to the bagging device 324. In the bagging device 324, the processed sludge is bagged for sale as fertilizer.

In another embodiment (not shown), the composter is replaced with a solids dryer 218 in which hot exhaust from the internal combustion engine 138 is used to dry the sludge taken from the solids press 214. Again, from the solids dryer 218, the activated sludge 184 is transferred to a bagging device 324. In the bagging device 324, the processed sludge is bagged for sale as fertilizer.

FIG. 12 illustrates another embodiment of the waste processing system of the present invention, wherein like elements have like numerals. Specifically, FIG. 12 illustrates a waste processing system 10′, which includes a digester enclosure 20′, a mixing chamber 30′, a digester 40′ and a clarifier 50′. A center wall 65′ divides the digester 40′ into a first leg 166′ and a second leg 170′. The sludge 144 can therefore move from the mixing chamber 30′ into the digester 40′ along the first leg 166′ in a first direction, and toward the clarifier 50′ along the second leg 170′ of the digester 40′ in a second direction opposite the first direction.

The first leg 166′ and the second leg 170′, as illustrated in FIG. 12, each include a partition 370 positioned relative to the center wall 65′ such that a space 380 is created between the partition 370 and the center wall 65′. The partition may comprise at least one of a rigid board or plank, curtain or drape, tarp, film, and a combination thereof. In addition, the partition may be constructed of a variety of materials, including without limitation, at least one of a metal, wood, polymer, ceramic, composite, and a combination thereof. The first leg 166′ and the second leg 170′ each further include a heating device 372 positioned within the space 380 between the partition 370 and the center wall 65′ such that sludge 144 or activated sludge 184 (referred to from this point forward as sludge 144 for simplicity) is heated as it contacts the heating device 372. Heated sludge 144 rises relative to cooler sludge 144 by free convection and is allowed to rise upwardly within the space 380.

The heating device(s) 372 and the partition(s) 370 are shown in greater detail in FIGS. 13 and 14. For simplicity, one of the heating devices 372 and the partitions 370 will be described in greater detail, but it should be noted that the description may equally apply to the other heating device 372 and partition 370. As shown in FIGS. 13 and 14, the heating device 372 includes a series of conduits 374, each containing a heating medium. A variety of heating media may be used with the present invention, including at least one of water and a gas. The conduits 374 do not all need to contain the same heating medium. That is, some of the conduits 374 may contain a gas, while others contain a liquid, such as water.

As illustrated in FIGS. 13 and 14, the waste processing system 10′ may further include at least one conduit 378, which contains a compressed, recycled biogas from the biogas storage area 59 and has nozzles 376. The nozzles 376 are gas outlets. The compressed biogas contained in the conduit 378 flows through the conduit 378 and out the nozzles 376, such that as the gas escapes the conduit 378 via the nozzles 376, the gas is propelled upwardly in the space 380 to promote the sludge 144 to move upwardly through the principle of air/water lifting. FIGS. 13 and 14 illustrate two conduits 378 having nozzles 376. Any number of conduits 378 having nozzles 376 can be used without departing from the spirit and scope of the present invention. The nozzles 376 may be simple holes drilled into conduit 378 or may be specialized nozzles 376 attached to conduit 378 via welding or tapping.

Referring to FIGS. 13 and 14, a frame 364 is positioned within the space 380 to support the heating device 372 and the conduits 378. The frame 364 is illustrated as comprising a plurality of ladder-like units 365 and a connecting bar 369 running generally parallel to the center wall 65′ to connect the units 365. Each unit 365, as illustrated in FIGS. 13 and 14, is formed of two vertical columns 366 positioned on opposite sides of the space 380 and a plurality of crossbeams 368 connecting the two vertical columns 366 across the space 380. The frame 364 is illustrated by way of example only, and the present invention is in no way limited to the illustrated support structure. A variety of frame elements can be used to support the heating device 372, conduits 378, and/or other components of the waste processing system 10′ within the space 380 without departing from the spirit and scope of the present invention.

As illustrated in FIGS. 13 and 14, the partition 370 has a top edge 371 and a bottom edge 373. In addition, the illustrated partition 370 is substantially vertical and shorter in height than the digester 40′, such that heated sludge 144 can move over the top edge 371 of the partition 370 and out of the space 380 between the partition 370 and the center wall 65′, and cooled sludge 144 can move under the bottom edge 373 of the partition 370 and into the space 380. Therefore, as illustrated by the arrows in FIGS. 13 and 14, the partition 370, in conjunction with the heating device 372, promotes upward and downward movement of the sludge 144. This upward and downward movement of the sludge 144 results in an overall spiral movement of the sludge 144 as the sludge 144 is moved along the first and second legs 166′, 170′ of the digester 40′. Further promoting this spiral motion are the two conduits 378 with nozzles 376, which are located beneath the series of conduits 374 of the heating device 372 in FIGS. 13 and 14. The spiral motion of the sludge 144 throughout the digester 40′ promotes thermal mixing of the sludge 144 to produce activated sludge 184.

The series of conduits 374 illustrated in FIGS. 12-14 is formed by having a two-by-five configuration within the space 380 (i.e. two conduits 374 across and five conduits 374 up and down), with the conduits 374 running generally parallel to the center wall 65′. Another example is a two-by-six configuration, as shown in FIG. 13. In addition, two conduits 378 having nozzles 376 also run generally parallel to the center wall 65′ and are positioned beneath the series of conduits 374 just described. It should be noted, however, that any number of conduits 374 containing heating medium, and any number of conduits 378 having nozzles 376 arranged in a variety of configurations can be used without departing from the spirit and scope of the present invention. The series of conduits 374 and the conduits 378 having nozzles 376 depicted in FIGS. 12-14 are shown by way of example only.

FIG. 15 illustrates a waste processing system 410 used to process high-solids waste according to another embodiment of the invention. A digester enclosure 420 includes three sections: a mixing chamber 430, a digester 440, and a clarifier 450. The digester enclosure 420 is arranged such that a relatively large digester 440 may be built in relatively small space.

As illustrated in FIG. 15, an outer wall 454 of the digester enclosure 420 is generally circular, such that an outer perimeter of the digester enclosure 420 is generally circular as well. Furthermore, the outer wall 454 forms at least a portion of the outer perimeter of the mixing chamber 430, digester 440 and clarifier 450. In other words, each of the mixing chamber 430, digester 440 and clarifier 450 has an outer perimeter defined by the generally circular outer wall 454 of the digester enclosure 420.

The mixing chamber 430 includes an influent pipe 448 for receiving waste material from outside of the digester enclosure 420 into the mixing chamber 430. A cutout 460 is formed in a wall 462 between the mixing chamber 430 and the digester 440 to allow sludge to flow from the mixing chamber 430 into the digester 440. The mixing chamber 430 also includes a heating device for preheating the sludge as it flows through the mixing chamber 430. The heating device may, for example, be a heating pipe 442 or other conduit containing a liquid or gas. The heating device 442 may include discharge nozzles (not shown) to further agitate the sludge.

The digester 440 includes a first leg or passageway 441, a second leg or passageway 442 and a third leg or passageway 443. The first and second passageways 441, 442 are separated from one another by a first divider 444, while the second and third passageways 442, 443 are separated from one another by a second divider 445. The first passageway 441 has a first end 441 a and a second end 441 b, the second passageway has a first end 442 a and a second end 442 b, and the third passageway 443 has a first end 443 a and a second end 443 b. The first end 441 a of the first passageway 441 is adjacent the cutout 460, which thus also serves as an inlet for receiving sludge into the digester 440. The second end 441 b of the first passageway 441 is adjacent the first end 442 a of the second passageway 442. The second end 442 b of the second passageway 442 is adjacent the first end 443 a of the third passageway 443. The second end 443 b of the third passageway 443 is adjacent the clarifier 450. The first divider 444 has an end 444 a around which the sludge flows from the first passageway 441 to the second passageway 442. Likewise, the second divider 445 has an end 445 a around which the sludge flows from the second passageway 442 to the third passageway 443. From the digester 440, the waste flows into the optional clarifier 450.

The digester 440 forms a flow path for the sludge that is generally S-shaped. It should be noted, however, that additional dividers could be employed to increase the length of the flow path, by adding additional passageways. The digester 440 provides a relatively long flow path for the sludge within the relatively small area enclosed by the outer wall 454.

The waste material processing system 410 as illustrated in FIG. 15 may include any of the features discussed with respect to the previous embodiments. For example, the digester 440 may include a heating device for heating the waste material as it flows through the digester 440. In one embodiment, the heating device includes heating pipe 478 arranged along one or both of the dividers 444, 445 within the first passageway 441, the second passageway 442, the third passageway 443, or a combination thereof. The digester heating pipes 478 locally heat the sludge using, for example, hot water or gas, causing the heated mixed sludge to rise under convective forces. The convective forces cause the heated sludge to rise near the first and second dividers 444, 445. At the same time, sludge near the relatively cooler outer wall 454 falls under convective forces. As a result, the convective forces cause the sludge to follow a circular flow path through the first passageway 441 upward along the divider 444 and downward along the outer wall 454. Likewise, the convective forces cause the sludge to follow a circular flow path through the third passageway 443 upward along the second divider 445 and downward along the outer wall 454. At the same time, the sludge flows along the first, second and third passageways 441, 442, 443, resulting in a combined corkscrew-like flow path for the sludge. The heating pipes 478 may include jet nozzles to dispense water or gas into the sludge. In another embodiment, hot gas injection jets using heated gases from the output of the engine (not shown) replace the hot water digester heating pipes as a heating and current-generating source. The injection of hot gases circulates the sludge through both natural and forced convection. A similar corkscrew-like flow path is thereby developed in the digester 440.

FIG. 16 illustrates another embodiment of the waste processing system of the present invention, wherein like elements have like numerals relative to the embodiment generally shown in FIG. 15. Specifically, FIG. 16 illustrates a waste processing system 410′, which includes a digester enclosure 420′, a mixing chamber 430′, a digester 440′ and a clarifier 450′. A first divider 444′ and a second divider 445′ divide the digester 440′ into a first passageway 441′, a second passageway 442′ and a third passageway 443′.

The digester 440′ further includes one or more partitions 370′ positioned relative to the first divider 444′ and the second divider 445′ such that a space 380′ is created between the partition 370′ and the respective divider. The partition 370′ may comprise at least one of a rigid board or plank, curtain or drape, tarp, film, and a combination thereof. In addition, the partition 370′ may be constructed of a variety of materials, including without limitation, at least one of a metal, wood, polymer, ceramic, composite, and a combination thereof. The first passageway 441′ and the third passageway 443′ each further include a heating device 478′ positioned within the space 380 between the partition 370′ and the dividers such that sludge is heated as it contacts the heating device 478′. Heated sludge rises relative to cooler sludge by free convection and is allowed to rise upwardly within the space 380′.

The illustrated partition 370′ is substantially vertical and shorter in height than the digester 440′, such that heated sludge can move over the top edge of the partition 370′ and out of the space 380′ between the partition 370′ and the divider, and cooled sludge can move under the bottom edge of the partition 370′ and into the space 380′. Therefore, the partition 370′, in conjunction with the heating device 478′, promotes upward and downward movement of the sludge. This upward and downward movement of the sludge results in an overall spiral movement of the sludge as the sludge is moved along the first passageway 441′, second passageway 442′ and third passageway 443′ of the digester 440′. Optionally, the second passageway 443′ includes the heating device 372′ and/or partition 370′ on either or both of the first divider 444′ and second divider 445′.

Various embodiments of the invention are set forth in the following claims. 

1. A method for the anaerobic digestion of waste material comprising: providing a closed container having a relatively circular outer wall, the closed container including a first passage having an inlet in which the waste material flows in a first direction, a second passage in which the waste material flows in a second direction, and a first divider having an end, the first divider separating the first passage from the second passage, a third passage in which the waste material flows in a direction substantially similar to the first direction of the first passage, and a second divider having an end, the second divider separating the second passage from the third passage, the waste material flowing around the end of the first divider when flowing from the first passage to the second passage and around the end of the second divider when flowing from the second passage to the third passage.
 2. The method of claim 1, wherein the first passage or the second passage includes at least a portion of the relatively circular outside wall.
 3. The method of claim 1, further comprising using a heating device positioned in the first or the second passage to induce the waste material to move in a corkscrew-like fashion through at least one of the first passage and the second passage.
 4. The method of claim 3, wherein the heating device is positioned adjacent the relatively circular outside wall and the heating device provides convective forces that cause heated waste material to rise near the relatively circular outside wall.
 5. The method of claim 3, wherein the heating device includes heating pipes, and further comprising enhancing convection and facilitating the corkscrew-like flow path with heating pipes.
 6. The method of claim 3, wherein the heating device is positioned adjacent the divider and the heating device provides convective forces that cause heated waste material to rise near the divider.
 7. The method of claim 3, wherein the heating device includes a conduit having at least one gas outlet positioned to promote upward movement of the heated waste material utilizing recycled bio gas.
 8. An anaerobic digester for digesting waste material comprising: a relatively circular closed container having a first passage in which the waste material flows in a first direction and a second passage in which the waste material flows in a second direction relatively opposite the first direction, the first passage being separated from the second passage by a first divider, and a third passage in which the waste material flows in a direction substantially similar to the first direction of the first passage, the second passage being separated from the third passage by a second divider.
 9. The anaerobic digester of claim 8, further comprising a mixing chamber positioned prior to the first passage and configured to preheat the waste material prior to the waste material entering the first passage.
 10. The anaerobic digester of claim 8, further comprising a clarifier chamber positioned after the third passage and configured to allow the waste material from the second passage to settle into liquid and solid components.
 11. The anaerobic digester of claim 8, further comprising a heating device to heat the waste material, the heating device positioned in the first passage, the second passage, or a combination thereof, to induce the waste material to move in a corkscrew-like fashion through at least one of the first passage and the second passage.
 12. The anaerobic digester of claim 11, wherein the heating device includes heating pipes configured to enhance convection and facilitate the corkscrew-like flow path.
 13. The digester of claim 8, further comprising a partition positioned relative to the one or more walls such that a space is created there between, and wherein a heating device is positioned within the space for heating the waste material and enabling heated waste material to flow upwardly within the space.
 14. The digester of claim 13, wherein the partition has a top edge over which heated waste material moves out of the space.
 15. The digester of claim 13, wherein the partition has a bottom edge under which waste material moves into the space.
 16. A closed anaerobic digester for digesting waste material comprising: a first section configured to receive the waste material from a source outside of the closed anaerobic digester and to preheat the waste material, the first section having an outer perimeter formed at least in part in the shape of a circle; and a second section configured to receive the preheated waste material from the first section and to anaerobically digest the preheated waste material, the second section having a first passage and at least one second passage separated from the first passage by one or more dividers, and a partition having a top edge and a bottom edge, the top edge being spaced a distance from a top of the closed second section, and the bottom edge being spaced a distance from a bottom of the closed second section, wherein the waste material changes direction upon flowing from the first passage to the at least one second passage, the second section having an outer perimeter formed at least in part in the shape of the same circle as the first section.
 17. The anaerobic digester of claim 16, further comprising a third passage, the waste material moving in a first direction in the first passage, the waste material moving in a second direction relatively opposite the first direction in the second passage, the waste material moving in a third direction substantially the same as the first direction in the third passage.
 18. The anaerobic digester of claim 16, further comprising a third section configured to received the waste material from the second section and to allow the waste material from the second section to settle into liquid and solid components, the third section having an outer perimeter formed at least in part in the shape of the same circle as the first and second sections.
 19. The anaerobic digester of claim 16, further comprising an outer wall in the shape of a circle and defining the outer perimeter of the first and second sections.
 20. The anaerobic digester of claim 16, further comprising a heating device positioned in the second section configured to induce convection of the waste material flowing through the first passage or the at least one second passage.
 21. The anaerobic digester of claim 20, wherein the heating device is positioned adjacent the outer wall.
 22. The anaerobic digester of claim 20, wherein the heating device is positioned adjacent one or more of the one or more dividers.
 23. The anaerobic digester of claim 20, wherein the heating device includes heating pipes configured to enhance convection and facilitate the corkscrew-like flow path.
 24. The anaerobic digester of claim 20 wherein the heating device is configured to heat the waste material with a gas. 